This invention relates to a protective device which finds application in a fluid-operated percussion tool and is of the type that has a housing portion which is coupled with the percussion tool and which shields the latter at least from the front against external effects. A tool bit driven by the percussion tool extends into the housing portion which, at its passage for the tool bit, has an external seal surrounding the tool bit with a small clearance transversely to the longitudinal tool bit axis and is movable transversely to the tool bit axis.
Fluid-driven percussion tools whose tool bit is usually a one-piece, chisel-like member are preponderantly used for breaking up rocks or stone formations. During such an operation, apart from large pieces of broken material, stone dust and grains of a few mm of diameter are also obtained. Since such a stone dust in most cases contains abrading material (such as quartz), its penetration into the tool bit guide causes an increased wear and possibly a premature breakdown of the structural elements.
For the protection of the tool bit guide against the penetration of dirt it has been known to use elastic sealing elements which, by being urged with their contact faces against the tool bit, seek to prevent penetration of small-size dirt (even down to dust consistency) . Such protective devices are, however, easily damaged during heavy duty use and further, they are exposed to significant wear due to the continuous reciprocating motion of the tool bit.
German Offenlegungsschrift (application published without examination) 34 40 530 describes a machine-guided percussion tool of the earlier-discussed type which is entirely encapsulated and has an outwardly shielding, disk-like damping element externally of the tool bit (chisel) guide. The percussion tool proper is countersupported by the surrounding housing with the interposition of elastic damping elements.